The invention relates to air dryers for air brake systems used on trucks and the like, and more particularly to improvements providing a substantially increased life rating and a substantial reduction in size and weight.
In air brake systems for trucks, air is typically supplied from an air compressor at the intake side of the truck engine. The air is supplied to an air dryer and then to an air tank and then to the air brakes. The air dryer is needed to remove water from the air brake lines and hence prevent problems of brake line freeze in winter, as well as other damage caused by water in the lines.
Air dryers typically use desiccant to absorb the water. While desiccant works well initially, it loses its absorption capability with time and becomes less effective. Furthermore, there is some oil in the air from the compressor, and the desiccant becomes coated with oil and further loses its absorption capability.
The housing for the desiccant is large and heavy because the larger the size the more desiccant can be accommodated. A disadvantage of this large size is that the air compressor must first fill the air dryer housing before it fills the air tank, and hence the larger the air dryer housing size the longer time it takes to fill or refill the air tank, which may be unacceptable for certain brake systems. A further disadvantage of the large size is that it limits the number of places on the truck where the air dryer can be mounted. A given truck may have adequate room at a certain place, while another truck may only have adequate room at another place, thus requiring different mounting locations, hardware arrangements, etc. for different trucks. This individual custom mounting is not cost effective. Furthermore, the large size adds considerable weight, a typical weight being about 34-39 pounds.
The present invention provides significant improvements in size and weight reduction, the preferred embodiment weighing about seven pounds. The size reduction enables the air dryer and hence the air tank to quickly fill or refill. Furthermore, the size reduction enables a universal mounting location and arrangement for numerous trucks, reducing installation time and expense.
The invention further eliminates the need to use desiccant, and provides substantially extended life. Separate heat exchange and filter sections are provided and in the preferred embodiment connected together in an integral housing. The heat exchanger cools the air from the compressor from 300.degree.-400.degree. F. to within a few degrees of ambient temperature, condensing and separating water from the air. The air then travels to a downstream water repellant filter permitting air flow therethrough but blocking water to separate drops of water from the air which have not dropped off previously and separating oil and other solids from the air. A pressure responsive valve communicates with the outlet of the heat exchanger and the inlet of the filter and discharges water condensed from the heat exchanger and repelled by the filter each time the compressor cycles at the lower and upper limits of its operating range at cut-in and cut-out. The air dryer operates for hundreds of hours between filter changes. The air dryer construction permits ready access and filter removal, for reduced maintenance expense.